Device for cooling hot rolled metallic strips

ABSTRACT

Device for cooling hot-rolled metallic strips, by means of water directed against the rapidly moving strip, between the last finishing stand of the mill and the coiler, comprising: MEANS CAPABLE OF DELIVERING A CONTINUOUS WATER FILM, WITH VERY LOW TURBULENCE, LIMITED THICKNESS AND WITH A LENGTH EXCEEDING GREATLY THE SAID THICKNESS. MEANS CAPABLE OF CONTROLLING THE FLOW RATE OF THE SAID WATER FILM WITHIN A CONSIDERABLE RANGE. MEANS CAPABLE OF ORIENTING PROPERLY THE SAID WATER FILM AGAINST THE STRIP.

United States Patent [191 Bertolotti et al.

[ Dec. 24, 1974 DEVICE FOR COOLING HOT ROLLED METALLIC STRIPS Inventors:Nino Bertolotti, Tirrenia; Bruno Sabatini; Giuseppe Mocci, both of Rome,all of Italy Centro Sperimentale Metallurgico S.p.A.

Filed: July 10, 1972 Appl. N0.: 270,292

Assignee:

Foreign Application Priority Data July 17,1971 Italy 51720/71 June 22,1972 Italy U 51091/72 US. Cl 266/3 R, 134/64, 266/4 S, 266/6 S, 239/590Int. Cl C21d l/62 Field of Search 266/3 R, 4 S, 6 R, 6 S;134/64,122,198;l48/143,153,156; 239/590, 590.3, 590.5, 456, 597

References Cited UNITED STATES PATENTS 4/1921 Sundh 134/64 3,208,7429/1965 Peretick 266/3 R X 3,554,513 l/l97l Chance 266/3 R 3,659,4285/1972 Kunioka et al. 266/6 s UX FOREIGN PATENTS OR APPLICATIONS 272,4333 1930 ltaly 266/6 s Primary Examiner-Roy Lake Assistant Examiner-PaulA. Bell Attorney, Agent, or FirmYoung and Thompson [57] ABSTRACT 18Claims, 11 Drawing Figures Pmmwmw 3.856.281

sum 2 er 5 15 2o 20 20 F/G.4

PATENIEBHEBM H 3,856,281

SHEET 5 BF 5 FIG. I F/GJO DEVICE FOR COOLING HOT ROLLED METALLIC STRIPSThe present invention relates to a device for cooling hot-rolledmetallic strips, and more particularly to a device for conveying waterunder pressure onto the strip in the form of a continuous thin film atvery low turbulence and at an optionally controllable flow rate, thesaid device being suitable for advantageous utilization as a componentof the runout cooling table between the last finishing stand of the hotstrip mill and the coiler.

As is known, in metal strip hot-rolling the apparent strip temperatureemerging from the last rolling stand is quite high, (in the case ofsteel it ranges from 850 to 950C), and before being coiled the stripmust be cooled down to a proper temperature according to its thicknessand to the metal involved (in the case of steel the temperature aftercooling ranges from 550 to 750C). This cooling is realized when thestrip passes over the runout table, along which it is subjected to watersprays. The length of this cooling section depends, other conditionsbeing equal, on three fundamental parameters: the strip speed, thecooling efficiency (Kcal/kg of H and the water flow rate, in the sensethat for a given strip speed, which in general is a fixed parameter, andfor each thickness of the strip to be processed and each thermaldifference to be realized, the length of the table increases if theefficiency and/or the flow rate decrease.

The cooling devices known in the art are essentially of the followingtypes:

a. Spray system. This consists of a number of manifolds from which somenozzles branch off to deliver water under pressure, atomized into moreor less minute particles. Each one of the said nozzles diverges by acertain angle, which determines a well defined impact area of the sprayson the strip to be cooled. The specific flow rates of the variousinstallations which are invariable for each installation range from 18to 30 m /h.m with a cooling efficiency of about 20 Kcalories per kg ofwater used. The extent of the impact area of a single water spray andthe required thermal drop, together with the amount of heat to beremoved, the specific flow rates and the cooling efficiency, alldetermine the number of water sprays necessary and hence the length ofthe cooling section.

In this type of installation, the cooling efficiency is criticallylinked with the specific flow rate of the nozzles in that, outside ofthe optimal flow rates pertinent to the type of the nozzles used, thecooling efficiency diminishes very rapidly; it is necessary, therfore,in view of qualitative and quantitative variations of the product, tooversize the installation and then to use it partially when working. Inthis way the cooling section is very long and the installation isminimally flexible, if a good cooling efficiency has to be maintained.

b. Laminar flow system. Essentially it consists of a certain number ofcylindrical tubes, set side by side and perpendicularly over the strip,and from which tubes, uniform cylindrical water streams flow with lowturbulence. The specific flow rates that are invariable for everyinstallation which this type of plant can deliver, are high (more than90 m /h.m with a cooling efficiency, of about Kcal/kg of water. Thissystem too has the drawback of low flexibility, whereby it is necessaryto oversize and subsequently to use the installation partially whenworking.

The aforesaid drawbacks are serious because the frequent need ofincreasing the productivity of an existing line and of varying theproduct mix makes it desirable to have a system more efficient andflexible than the existing ones, because very often for economic reasonsor owing to lack of space it is not possible to increase the length ofthe runout cooling table.

It is an object of the present invention to supply a device whicheliminates the drawbacks of the cooling systems used hitherto.

Another object of the present invention is to supply a device forcooling hot-rolled metallic strips allowing high specific water flowrates and a good cooling efficiency, thus allowing for a reduced lengthof the cooling runout tables.

A further object of the present invention is to supply a device forcooling hot-rolled metallic strips capable of supplying water in theform of a film with limited thickness, very low turbulence, and atoptionally and continuously controllable flow rates within a wide range,the said device allowing the delivery of even considerably differentflow rates while maintaining an acceptable cooling efficiency.

Another object of the present invention is to supply a device forcooling of hot-rolled metallic strips, capable of effecting a cooling ofsaid strip more rapid than what was possible hitherto and such as toestablish a finer grain structure in the strip, thus reducing theduration of the subsequent thermal treatments and making the subsequentcold rolling easier.

However, it should be observed that the structural complexity andmoreover, the overall dimensions and finally the greater cost of such adevice, do not suggest its use whenever the cooling devices have to workfor rather long periods, as happens most frequently, under constantoperating conditions, that is, for the sheets or strip which do notpresent noticeable variations of dimensions during the same period.

Therefore, as it is not necessary, in this case, to regulatecontinuously and with sufficient rapidity the flow rate of the coolingfluid, it is possible and advisable to adopt a second, simpler, sturdiertype of cooling device, with smaller overall dimensions, which, whileguaranteeing a sufficiently rapid cooling needed to establish a finegrain structure in the strip, by reducing the time of the subsequentthermal treatments and by making the subsequent cold rolling easiernevertheless eliminates the drawbacks already mentioned in the case ofthe first type of the device.

Therefore, a specific object of the present invention is also a devicefor cooling hot-rolled metallic strips in mills operating at constantconditions, on a strip with substantially constant dimensions, by meansof a water flow over the rapidly moving strip, between the lastfinishing stand of the hot rolling mill and the first coiler, whichcomprises: means suitable for delivery of a continuous film of waterwith low turbulence and limited thickness, the length of which exceedsgreatly the said thickness. means suitable for orienting the said waterfilm with respect to the strip.

The delivering means comprise a distributing box, without the regulationblade or septum, and defined in its inside by two longitudinal lateralwalls with a profile symmetrical with respect to the median verticalplane of the outflow section, which compel the cooling water to follow apath with a gradually decreasing cross section. The solution suggestedfor effecting the said decreasing shape of the outflow section, consistsin shaping directly the longitudinal lateral walls of the box, whileavoiding thickenings or protrusions, by adopting for them a curvaturedefined by regular arcs of circle so that the plane tangential to theprofile surface of the wall, at the edge of the outflow slit, forms anangle ranging from to 10 with the vertical plane of symmetry.

This solution does not preclude, in any event, the possibility of aregulation of the flow rate, in relation to the variations of therolling schedules, because the device can be integrated with elementssuitable to vary the section of the outflow, as it will be describedhereinafter.

The present invention will not be described with reference to thedrawings, which are herein attached only as an example and not in alimitative way, wherein:

FIG. 1 shows a distributing box;

FIG. 2 shows an inside view of the said distributing box, without theconveying blade or septum;

FIG. 3 shows a cross section of the said distributing box with theconveying septum;

FIG. 4 schematically shows a cooling runout table of a hot rolling mill,in order to indicate various possible arrangements of the saiddistributing boxes with respect to the vertical plane normal to thestrip;

FIG. 5 gives a schematic view from the top, of a portion of the runoutcooling table to show a possible angulation of the said distributingboxes;

FIG. 6 shows a section of a distributing box, with several internalsepta, the end ones being in closing position;

FIG. 7 gives a schematic view from the top, of a portion of the runoutcooling table in the case when the length of each single distributingbox is inferior to the width of the strip;

FIG. 8 is an exploded view of a further embodiment of a distributingbox, according to the invention;

FIG. 9 is an internal, partially sectioned, perspective view of a stillfurther embodiment of distributing box;

FIG. 10 is a vertical section of a fragment of the box indicated in FIG.8; and

FIG. 11 is a vertical section view of a second regulation member of theflow section of the box indicated in FIG. 8.

The device according to the present invention, comprises essentiallymeans to deliver a low turbulence water film with controllable thicknessand a length exceeding greatly its own thickness. (By length is hereinintended the maximum dimension of the water film paralleling the strip).With the aforesaid means are included, cooperate means to control,within a considerable range, the flow rate of the said water film andmeans to orient properly the said water film with respect to the strip.

The said means, to deliver a water film comprise a distributing box 1,constituting a repetitive module for the whole width of the runoutcooling table, supplied with piping for water inlet 2, a septum or blade3 to control the flow rate of the said water film, with devices 4, knownin the art, for the vertical displacement of the said septum or blade inthe inside of the said distributing box 1, and with means 5, alsoalready known, for properly orienting the said water film with respectto the strip to be cooled. According to the present invention, the saiddistributing box 1 is supplied on the wall 6 facing the strip with alongitudinal slit 7 wherein the said septum or blade 3 is inserted. Thelongitudinal edges 8 of the said slit are prolonged into the lateralwalls 9 of the said box, by protrusions 10, having a transverse sectiondeparting from the junction of the said protrusions, to the lateralwalls of the said box initially with a profile concave towards theinside of the said box, with a curvature increasing as far as theinflection point, located at about one third of the protrusion heightfrom the wall 6 of the box facing the strip and, beyond an inflextionpoint, the said protrusions are terminated on the longitudinal edges 8of the said slit 7 with a sharp edge, in such a way that the tangent tothe profile of the said protrusion 10, at its intersection with the edge8 of the said slit, forms an angle ranging from 65 to 88 with the wall 6facing the strip.

The said protrusions can be inserted into the box and fixed to it, orthey can be obtained from the box lateral walls 9 themselves, properlyshaped for instance by forming or by other means suitable for thispurpose.

The said box is orientable with respect to the strip, in such a way thatthe water film delivered by it can impinge on the strip at variousangles with respect both to the vertical and to the width of the stripitself. The dimensions of the said box are such that its height andlength ratio, and its width and the said height ratio, range from 1 to0.1, these two ratios, however, being not equal in general to eachother.

Also according to the present invention, the said protrusions are sizedin such a way that their height, as measured along the lateral walls 9of the said box, ranges from to l 15 percent of the width of the boxitself, while their maximum width, as measured along the wall 6 of thesaid box, facing the strip, at the edge 8 of the longitudinal slit 7,ranges from 25 to 45 percent of the said width of the box. The saidlongitudinal slit 7 on the wall 6 facing the strip of the said box, hasa length equal to that of the said wall 6, and has a width ranging from10 to 50 percent of the width of the box itself.

In the said longitudinal slit 7 there is inserted a septum or blade 3which is as long as the said slit and which defines, with the edges 8 ofthe same, two longitudinal openings 11 from which the cooling waterflows as two slightly convergent streams which join at the outlet edge12 of the said septum 3, producing a water film having the requiredcharacteristics (limited thickness and laminar flow). The said septum orblade is symmetrical with respect to its own longitudinal center plane,and presents a cross section departing from the leading or junction edge13 with the fluid stream initially with a convex profile, withincreasing curvature as far as a maximum located from one-third toone-fourth of the height of the same septum from its upper edge l3,which is the said junction edge of the fluid stream, and then with adecreasing curvature to an inflection point beyond which the profile isslightly concave.

The symmetrical profiles of the said septum or blade 3, are such thattheir upper edges meet at an angle ranging from 50 to and their lower ortrailing or outlet edges 12 meet at an angle ranging from 4 to 20.

The said septum or blade, inside the said box, has its own longitudinalsymmetry plane coinciding with the longitudinal center plane of the box,and it is movable, along the said longitudinal symmetry plane, in such away as to vary, with a displacement ranging from to 100 mm, the crosssection of the said openings 11 from the maximum to the minimum value atwhich the said openings are completely closed. In the maximum openingposition, the total available cross section for the water outflow whichis the sum of the existing spaces located between the said septum andthe two longitudinal edges of the said slit ranges from 10 to 50 percentof the area of the said slit.

According to the present invention, the hereinbefore described device isadvantageously utilized to convey over the hot strip, a water film oflimited thickness with very low turbulence, and with a length tothickness ratio ranging from 10 to 500.

Furthermore, the said box may preferably cover the entire width of thecooling runout table, and in this case it protrudes from both edges ofthe strip by an extent ranging from 5 to 25 percent of the width of thestrip itself. In case the rolling schedule calls for the cooling ofstrips with very different widths, it is clear that a distributing box,having adequate dimensions for the widest strip would be excessive forthe most narrow strip, causing a considerable waste of water. Thisdrawback can be advantageously eliminated by placing the said box in asharply angulated position with respect to the width of the strip, or bydividing the septum or blade of the box into at least three smallersepta, 3,3',3" (see FIG. 6) in such a way as to close completely thedelivery in the end zones of the box, or finally by placing a group ofboxes, whose length is shorter than the width of the cooling bed, on thewidth of the bed itself, covering its entire width, the external boxesof the said group being positioned in such a way as to protrude beyondthe edges of the wider strip to be rolled by a value ranging from 5 to25 percent of the width of the said strip. The said group consists atleast of three boxes which can be placed as shown in FIG. 7, wherein 24indicates the group of such smaller boxes.

According to the present invention, a plurality of said water streams 23are conveyed onto the moving strip, both from above and from below, asshown in FIG. 4, wherein the runout cooling table of a hot-rolling millis shown schematically, and wherein the last finishing stand of therolling mill is indicated by 14, the strip by 15, the rollers of therunout table where the said strip runs by 16, the coiler by 21, theseries of boxes placed below the strip by 20, and the boxes placed abovethe strip by l7, l8 and 19. According to the present invention, thedistributing boxes can be oriented properly, with respect to the strip,in such a way that the water films delivered by the boxes can impinge onthe strip at various angles, both with respect to the vertical, (asshown in FIG. 4, details 18 and 19), and with respect to the width ofthe strip itself, (as shown in H0. 5, detail 22). The said water films23, are delivered by the said distributing boxes at widely varyingpressures, the most convenient minimum pressure ranging from 0.01 to 1atmosphere gauge, and the maximum pressure ranging advantageously from 1to 10 atmospheres gauge.

Some practical tests on the first type of the device, according to thepresent invention, have been performed on a steel strip 600 mm wide and1.2 mm thick. The cooling bed consisted of 10 boxes, as described in thetext of the present specification. From a statistical average of theresults of these practical tests the following data have been obtained:

Specific flow rates m lhm 50 1 l0 18 230 Cooling efficiency Kcal/Kg H 014 16.2 l5 12 According to the aforementioned test results, the

cooling efficiency undergoes a decrement lower than 30 percent of thevalue of the optimal efficiency, for specific flow rates variationsranging from less than percent to more than 1 10 percent, with respectto the value of the specific flow rate corresponding to the said optimalcooling efficiency.

With particular reference to FIG. 8 of the attached drawings, there canbe observed the distributing box 25, with length l, heigth h, and widthb, which constitutes a repetitive module for the whole width of thecooling bed, wherein the water is introduced by piping 26, derived fromthe feeding manifold. The box 25 is provided, in this embodiment, in itslower portion, with a longitudinal slit 27, with a width a, defining theoutflow cross section. The longitudinal edges 28 of the said slit 27 areprolonged into the lateral walls 29 of the box '26, by two stretches ofwall 30 with a height 11,, which present a regular profile of two arcsof circle, symmetrical with respect to the vertical center plane of theslit 27. The said stretches of wall 30 end in the longitudinal edges ofthe outlet of slit 27, filleting in such a way that the tangent to thesaid shaped stretches of wall, at the intersection point with the saidedges, forms with the horizontal base plane of the slit, an angleranging from 80 to (O-l0 angle, with the vertical plane). The saidstretches of wall 30, shaped as an arc of circle, can be manufactured ina simpler manner, for example by rolling, than the protrusions of thedevice before described.

The distributing box 25 is orientable with respect to the strip so thatthe angle of the water film with respect to it can be varied.

The dimensions of the box, very much reduced in comparison of thatbefore described are such as to be able to define the following ratios:

h (height)/I (length) 0.05 l

b (width)/h (height) 0.1 l

h, (height of the shaped stretch wall)/b (width) 0.5 2

b (width)/a (outflow cross section) which the box has been built. Thecooling water is compelled to penetrate into the downflow zone (definedby two septa or walls 33, tilted downwards, with height h of width 2a,,comprising an upper inlet zone ending downwardly in an outflow slit 34with a width a. A blade 35, with a height h fixed to the upper wall ofpipe 32, penetrates into the outflow zone for a certain distance (kg/2),creating a partition wall for the distribution of the flow of theliquid.

The dimensions of the box, are defined by the following ratios:

b/l=0.05 1; h /b 0.1 0.95

bla= 5 50; h /b= 0.8; 2a /a= l 15 In FIGS. 10 and 11 are shown, in thetwo preferred embodiments, the members for the variation of the area ofthe cross section of outflow from the longitudinal slit.

Means are shown which permit the rotation (FIG. 10) of the shaped wall36 of the distributing box, or its translation (FIG. 11) perpendicularlyto the symmetry plane of the shaped walls.

In FIG. 10, the profile 36 ends, on the upper part, in a curved portion37 which is accomodated between two tightening surfaces, driven by thetightening pin 38 controlled by the tightening nuts 39, whereby it canbe given different adjusted positions.

In FIG. 11, the profile 36 ends, on the upper part, in a stretch 40 atan angle which can adopt, horizontally, different positions under thecontrol of the tightening group 41.

As an example and not as a limitation, the results of some experimentaltests performed on a 500 X 20 mm steel strip are reported. The coolingunit consisted of boxes. A cooling of the strip surface from 950C to550C has been obtained in the average time of 5-7 seconds, with anefficiency (degree of water utilization) of about 16 Kcal/kg of water.Summarizing, for the specific flow rates hereinbefore mentioned, thedata reported in the following table have been obtained:

Specific flow rates [20 I50 240 300 (m lm Exchang e intensity 3200 30003400 2900 (Kcal/m h C) Coolinlg efficiency l7 l5 I4 12 (Kcal/ .H O)

The present invention has been described and illustrated with referenceto various embodiments thereof, but it is intended that variations ormodifications may be introduced therein, without departing from thescope of the appended claims.

Having thus described the present invention, what is claimed is:

1. A device for cooling hot rolled metallic strip by means of waterdirected against a strip moving rapidly between the last finishing standof a strip mill and a coiler, comprising a cooling water distributingbox having inner side walls that converge downwardly and terminatedownwardly in a slit that extends generally transverse to the path ofmovement of the strip, said side walls having upper concave portions andlower convex portions adjacent said slit.

2. A device as claimed in claim 1, said concave portions beingsubstantially taller than said convex portions. I

3.'A device as claimed in claim 1, said inner side walls forming anangle of 65 to 88 to the horizontal at said slit.

4. A device as claimed in claim 1, and means to adjust the position ofsaid box vertically relative to a said path of movement of the strip.

5. A device as claimed in claim 1, and means to adjust the position ofsaid box so that said slit forms an adjustable angle with said path ofmovement of the strip.

6. A device as claimed in claim 1, and means for controlling the flowrate of water through said slit, said means comprising a blade disposedin the distributing box and extending downwardly into said slit, andmeans for vertically adjusting the position of the blade relative tosaid side walls.

7. A device as claimed in claim 6, said blade having downwardlyconverging outer side walls.

8. A device as claimed in claim 7, said blade having a cross-sectionalconfiguration which is symmetrical with respect to its verticalmidplane.

9. A device as claimed in claim 8, said blade having a cross-sectionalconfiguration which is substantially of tear-drop shape.

10. A device as claimed in claim 9, said tear-drop shape having a convexcurvature that increases downwardly for a minor portion of the height ofthe blade and then decreases to an inflection point below which saidouter side walls of said blade are concave.

11. A device as claimed in claim 6, said blade having upper edgesdisposed at an angle of 60 to 100 to each other and lower edges disposedat an angle of 4 to 20 to each other.

12. A device as claimed in claim 6, said blade occupying 50 to 90% ofthe width of said slit.

13. A device as claimed in claim 6, said blade being divided into atleast three pieces disposed side-by-side and individually verticallymovable independently of each other.

14. A device as claimed in claim 1, the upper portion of said box havinga circular cross-sectional configuration.

15. A device as claimed in claim 1, and means mounting said inner sidewalls for adjustive movement toward and away from each other.

16. A device as claimed in claim 1, and means for adjusting the angle ofsaid inner side walls relative to each other.

17. A device as claimed in claim 1, said box being elongated and havinga generally rectangular configuration and said other side walls beingdefined by protrusions disposed in said box, said protrusions havingsubstantially uniform cross-sectional configuration lengthwise of saidbox, said slit extending lengthwise of said box.

18. A device as claimed in claim 1, in which the water directed againstthe strip forms a continuous bandshaped flow having a widthsubstantially corresponding to the width of said strip.

1. A device for cooling hot rolled metallic strip by means of waterdirected against a strip moving rapidly between the last finishing standof a strip mill and a coiler, comprising a cooling water distributingbox having inner side walls that converge downwardly and terminatedownwardly in a slit that extends generally transverse to the path ofmovement of the strip, said side walls having upper concave portions andlower convex portions adjacent said slit.
 2. A device as claimed inclaim 1, said concave portions being substantially taller than saidconvex portions.
 3. A device as claimed in claim 1, said inner sidewalls forming an angle of 65* to 88* to the horizontal at said slit. 4.A device as claimed in claim 1, and means to adjust the position of saidbox vertically relative to a said path of movement of the strip.
 5. Adevice as claimed in claim 1, and means to adjust the position of saidbox so that said slit forms an adjustable angle with said path ofmovement of the strip.
 6. A device as claimed in claim 1, and means forcontrolling the flow rate of water through said slit, said meanscomprising a blade disposed in the distributing box and extendingdownwardly into said slit, and means for vertically adjusting theposition of the blade relative to said side walls.
 7. A device asclaimed in claim 6, said blade having downwardly converging outer sidewalls.
 8. A device as claimed in claim 7, said blade having across-sectional configuration which is symmetrical with respect to itsvertical midplane.
 9. A device as claimed in claim 8, said blade havinga cross-sectional configuration which is substantially of tear-dropshape.
 10. A device as claimed in claim 9, said tear-drop shape having aconvex curvature that increases downwardly for a minor portion of theheight of the blade and then decreases to an inflection point belowwhich said outer side walls of said blade are concave.
 11. A device asclaimed in claim 6, said blade having upper edges disposed at an angleof 60* to 100* to each other and lower edges disposed at an angle of 4*to 20* to each other.
 12. A device as claimed in claim 6, said bladeoccupying 50 to 90% of the width of said slit.
 13. A device as claimedin claim 6, said blade being divided into at least three pieces disposedside-by-side and individually vertically movable independently of eachother.
 14. A device as claimed in claim 1, the upper portion of said boxhaving a circular cross-sectional configuration.
 15. A device as claimedin claim 1, and means mounting said inner side walls for adjustivemovement toward and away from each other.
 16. A device as claimed inclaim 1, and means for adjusting the angle of said inner side wallsrelative to each other.
 17. A device as claimed in claim 1, said boxbeing elongated and having a generally rectangular configuration andsaid other side wAlls being defined by protrusions disposed in said box,said protrusions having substantially uniform cross-sectionalconfiguration lengthwise of said box, said slit extending lengthwise ofsaid box.
 18. A device as claimed in claim 1, in which the waterdirected against the strip forms a continuous band-shaped flow having awidth substantially corresponding to the width of said strip.